1. Field of the Invention
The present invention relates to a cellular radio telephone set and, more particularly, to a cellular radio telephone set having a USB (Universal Serial Bus) peripheral circuit which realizes a USB connection function.
2. Description of the Prior Art
Cellular radio telephone sets are desired to have reduced size and weight for portability, and their internal batteries are also reduced in size and weight. However, a small-size, light-weight internal battery means a short service life. The cellular radio telephone must always be ON to ensure a long standby time because the user does not know when he/she may receive an incoming call. Therefore, the cellular radio telephone set must reduce its power consumption to prolong the standby time.
Recent cellular radio telephone sets are connected to information processing terminal apparatuses such as a personal computer (to be simply referred to as a PC hereinafter) and a PDA (Personal Digital Assistants), realizing information exchange with the information processing terminal apparatuses and mobile communication using the telephone network of the cellular radio telephone set. At this time, the information processing terminal apparatus and cellular radio telephone set are connected using, e.g., a USB.
In the use of the USB, the cellular radio telephone set must be newly equipped with a USB peripheral circuit such as a USB device controller circuit. Power for operating the USB peripheral circuit is further required.
For the USB, a suspend mode is generally prepared. Using the suspend mode can reduce the power consumption of the USB peripheral circuit when the cellular radio telephone set is not connected to the information processing terminal apparatus.
Even the suspend mode cannot completely eliminate the power consumption of the USB peripheral circuit, and a current of about 500 mA may flow at maximum. Demands have arisen for a further improvement in this respect.